The present invention relates to a novel retrovirus from the HIV group which is presently designated more precisely as HIV subtype O, and to variants or parts thereof which contain the essential properties of the virus. A process is described for culturing the retrovirus. The invention furthermore relates to the isolation of this retrovirus and to the use of the virus, its parts or extracts for medicinal purposes, for diagnosis and in the preparation of vaccines.
In humans who are infected with them, retroviruses which belong to the so-called HIV group lead to disease symptons which are summarized under the collective term immunodeficiency or AIDS (acquired immune deficiency syndrome).
Epidemiological studies verify that the human immunodeficiency virus (HIV) is the etiological agent for the overwhelming majority of AIDS (acquired immune deficiency syndrome) cases. A retrovirus which was isolated from a patient and characterized in 1983 was given the designation HIV-1 (Barre-Sinoussi, F. et al., Science 220, 868-871 [1983]). A variant of HIV-1 is described in WO 86/02383.
A second group of human immunodeficiency viruses was identified in West Africa in 1985 (Clavel, F. et al., Science 233, 343-346 [19863]) and designated human immunodeficiency virus type 2 (HIV-2) (EP-A-O 239 425). HIV-2 retroviruses clearly differ from HIV-1 but are also related to monkey immunodeficiency viruses (SIV-2). Like HIV-1, HIV-2 also gives rise to an AIDS symptomatology.
New HI viruses, as represented by ANT70 (J. Vir., 1994, Vol. 68, No. 3, pp. 1586-1596) and MVP-5180/91 (J. Vir., 1994, Vol. 68, No. 3, pp. 1581-1585) have recently been described which can not be classified in HIV-1 subtypes A-F. Owing to their clear structural differences from the known HIV-1 strains, both isolates have provisionally been classified together under subtype O (G. Myers, Los Alamos Data Base), although they clearly differ from each other in their genomic nucleotide sequences.
It is a characteristic of human immunodeficiency viruses that they exhibit a high degree of variability which markedly complicates the comparability of the different isolates. When different HIV-1 isolates are compared, high degrees of variability are found, for example, in some regions of the genome whereas other genome regions are comparatively well conserved (Benn, S. et al., Science 230, 949-951 [1985]). HIV-2 ha3 also been reported to exhibit a very high degree of polymorphism (Clavel, F. et al., Nature 324, 691-695 [1986]). Regions in the gag and pol genes which encode proteins which are structurally and enzymatically essential possess the greatest genetic stability. By contrast, some regions in the env gene, and also the genes (vif, vpr, tat, rev, nef) which encode regulatory proteins, exhibit a high degree of variability.
It was furthermore demonstrated that antisera against HIV-1 also cross-react with HIV-2 gag and pol gene products even though only low sequence homologies were present. The hybridization between these two viruses was likewise of no great significance unless conditions of very low stringency were used (Clavel, F. et al., Nature 324, 691-695 [1986]).
Due to the wide distribution of the retroviruses from the HIV group, and to the fact that a period of from a few to many years (2-20) elapses between the time of infection and the time at which definite symptoms of pathological changes are recognizable, it is epidemiologically of great importance to ascertain infection with retroviruses of the HIV group at as early a stage as possible and, in particular, in a reliable manner. This is of importance not only in the diagnosis of patients who are exhibiting signs of immunodeficiency, but, even more so, in the screening of blood donors. It has emerged that when retroviruses, or components thereof, of the HIV-1 or HIV-2 type are used in detection systems, antibodies either cannot be detected or can be detected only weakly in some sera, even though signs of immunodeficiency occur in the patients from whom the sera are derived. In certain cases, such detection is possible using the HIV group retrovirus according to the invention.
The genotypic diversity of the HIV viruses presents a substantial problem for diagnosis in particular. In the case of the HIV-1 viruses, it is assumed that one nucleotide is changed per genome in each replication cycle. As a result of this genetic variability, the HIV viruses are able to respond in an extraordinarily flexible manner to the in-vivo selection pressure and to generate, extremely rapidly, mutants which either are resistant to pharmacological agents or are able to attack individuals who have built up a certain degree of immunological protection (Sharp et al., xe2x80x9cOrigins and diversity of human immunodeficiency virusesxe2x80x9d, AIDS 1994, vol. 8, Suppl. 1; S 27-S 42).
In order to prevent the spread of infections, in particular in association with blood transfusions but also in association with organ donations, it should be possible to ascertain an infection with an HIV virus with, if possible, 100% certainity. For this reason, it is also necessary diagnostically to detect those infections which are caused by a virus which, while currently only being distributed in certain geographical regions, is able without difficultyxe2x80x94unless suitable preventive measures are takenxe2x80x94to spread into Europe or the United States of America.
A description is given of the isolation and characterization of a novel human immunodeficiency virus, designated MVP-2901/94 hereinafter, which was isolated in 1994 from the peripheral lymphocytes of a 24 year old female patient from the Cameroons who was exhibiting signs of immunodeficiency. From the point of view of geography, this retrovirus originates from a region in Africa which is located between West Africa, where infection with HIV-2 and HIV-1 viruses is endemic, and East Africa, where it is almost exclusively HIV-1 which is disseminated. Consequently, the present invention relates to a novel retrovirus of the HIV subtype O group, which retrovirus is designated MVP-2901/94, and to its variants, to DNA sequences, amino acid sequences and constituent sequences derived therefrom, and to test kits containing the latter.
MVP-2901/94 can be propagated in the MT2 and Jurkat cell lines. The isolation and propagation of viruses are described in detail in the book xe2x80x9cViral Quantitation in HIV Infection, Editor Jean-Marie Andrieu, John Libbey Eurotext, 1991xe2x80x9d. The procedural methods described therein are incorporated in the disclosure of the present application by reference.
In order to provide a better understanding of the differences between the MVP-2901/94 virus according to the invention and the HIV-1 and HIV-2 retroviruses, the structure of the retroviruses which cause immunodeficiency will first of all be explained briefly. In the centre of the virus, the RNA is located in a conical core which is assembled from protein subunits which carry the designation p 24 (p for protein). This inner core is surrounded by a protein coat which is constructed from protein p 17 (outer core), and by a glycoprotein coat which, in addition to lipids, which originate from the host cell, contains the transmembrane protein gp 41 and the coat protein 120 (gp 120). This gp 120 then binds to the CD-4 receptors of the host cells.
As far as is known, the RNA of the HIV virusesxe2x80x94portrayed in a simplified mannerxe2x80x94possesses the following gene regions: so-called long terminal repeats (LTR) at each end, together with the following gene regions: gag, pol, env and nef. The gag gene encodes, inter alia, the core proteins, p 24 and p 17, the pol gene encodes the reverse transcriptase, the protease, the RNAse H and the intearase, and the env gene encodes the glycoproteins, gp 41 and gp 120, of the virus coat. The nef gene encodes a protein having a regulatory function. The arrangement of the genome of retroviruses of the HIV type is shown diagrammatically in FIG. 1.
The so-called PCR (polymerase chain reaction) has become a genetic manipulation method which has a multiplicity of possible uses, and the components which are required for implementing the method can be purchased. Using this method, it is possible to amplify DNA sequences if DNA regions of the sequence to be amplified are known. Short, complementary DNA fragments (oligonucleotides=primers) which anneal to a short region of the nucleic acid sequence to be amplified have then to be synthesized. For carrying out the test, HIV nucleic acids are introduced together with the primers into a reaction mixture which additionally contains a polymerase and nucleoside triphosphates. The polymerization (DNA synthesis) is carried out for a defined time, and the nucleic acid strands are then separated by heating. After cooling, the polymerization then proceeds once more. If, therefore, the retrovirus according to the invention is an HIV-1 or HIV-2 virus, it should be possible to amplify the nucleic acid using primers which are conserved within the known sequences of the HIV-1 and HIV-2 viruses. Some primers of this type have previously been described (Laurxc3xa9, F. et al., Lancet ii, (1988) 538-541 for pol 3 and pol 4, and Ou C. Y. et al., Science 239 (1988) 295-297 for sk 38/39, sk 68/69).
However, these primers are not able to amplify DNA from the VP-5180/91 HIV isolate (J. Vir., 1994, vol. 68, no. 3, pp. 1581-1585). Use of these primers likewise failed to amplify DNA from the MVP-2901/94 isolate, supporting the view that this isolate also diverges strongly from the HIV-1 consensus sequence. It was necessary, therefore, to construct a wide variety of new primers which were derived from known sequences and which were as strongly conserved as possible, and to use them in as many combinations as possible while varying the reaction conditions. Surprisingly, it was found that it was possible to amplify the DNA of MVP-2901/94, and thus gain a first lead into the sequence of the isolate, using a combination of the primers 212 and 412 which were derived from the sequence of the MVP-5180/91 isolate, under the reaction conditions given in Example 4.
Once a constituent region of the sequence of an HI virus has been decoded, as it has in the present case, the entire genome of the virus can be cloned and sequenced using known, standard molecular biological methods.
1) This can, for example, be achieved by cloning a cDNA in the following manner: the virus is precipitated from an appropriately sized culture volume (approximately 1 l) and resuspended in phosphate-buffered sodium chloride solution. It is then pelleted through a (20%) sucrose cushion. The virus pellet can be suspended in 6 M guanidinium chloride in 20 mM dithiothreitol and 0.5% Nonidet P 40. CsCl is added to a concentration of 2 molar, and the solution containing the disrupted virus is loaded onto a cesium chloride cushion. The viral RNA is then pelleted by centrifugation, dissolved, extracted with phenol and precipitated with ethanol and lithium chloride. The synthesis of the first cDNA strand is carried out on the viral RNA, or parts thereof, using an oligo(dT) primer. The synthesis, for which reverse transcriptase is added, can be carried out using a commercially available kit. For the synthesis of the second strand, the RNA strand of the RNA/DNA hybrid is digested with RNase H, and the second strand is synthesized using E. coli DNA polymerase I. Blunt ends can then be produced using T4 DNA polymerase, and these ends can be bonded to suitable linkers for restriction cleavage sites. Following restriction digestion with the appropriate restriction endonuclease, the cDNA fragment is isolated from an agarose gel and ligated to a vector which has previously been cut in a suitable manner. The vector containing the cDNA insert can then be used to transform competent E. coli cells. The resulting colonies are then transferred to membranes, lyzed and denatured, and finally detected by hybridization with nucleic acid which is labeled with digoxigenin or biotin. Once the corresponding cDNA has been prepared by genetic manipulation, it is possible to isolate the desired DNA fragments originating from the retrovirus. Incorporation of these fragments into suitable expression vectors then makes it possible for the desired protein or protein fragment to be expressed and employed for the diagnostic tests.
2) As an alternative to the stated method, the nucleic acid of the immunodeficiency virus can be cloned with the aid of PCR technology. To do this, it is necessary in each case to identify, from the still unknown region of the sequence, primers which can, in combination with the primers derived from the known part of the sequence, render it possible to amplify the DNA of the isolate.
3) A further possibility of cloning the virus by proceeding from the known sequence segment is that of cloning the proviral genomic DNA of the virus. For this purpose, genomic DNA from an infected cell line is first purified by standard methods. The proviral DNA, which is integrated into the host genome, can then be cloned after constructing and screening a genomic library. To do this, the genomic DNA is partially fragmented, and the fraction containing fragments of a length of about 10-25 kb is isolated and cloned into a vector system, such as cosmids or lambda phages, which is able to accommodate fragments of this length. Using the selected vector system, the mixture of the genomic fragments is transformed into an E. coli strain. Vectors which contain the viral genome can then be identified by hybridization with a cloned DNA fragment of the sought-after virus, which fragment is labeled radioactively or in some other way, and subsequently isolated (plaque screening or colony screening). The viral genome is thereby made available for sequence analysis and for expression of its proteins. The similarity between different virus isolates can be expressed by the degree of homology between the nucleic acid or protein sequences. 50% homology means, for example, that 50 out of 100 nucleotide or amino acid positions in the sequences correspond to each other. The homology of proteins is determined by sequence analysis. Homologous DNA sequences can also be identified by the hybridization technique.
The present invention therefore relates to an immunodeficiency virus of the. HIV group, or variants of this virus, which exhibits morphological and immunological properties which correspond to those of the retrovirus which is deposited with the European Collection of Animal Cell Cultures (ECACC) under No. V 95012601 and which has the designation MVP-2901/94. The date of deposition was Jan. 26th 1995.
The essential morphological and immunological properties of the immunodeficiency virus are understood to mean those structures which are of decisive importance for the immunological characterization of the virus. In this context, those epitopes are particularly crucial which give rise to an amplified production of antibodies in infected persons and which are suitable for dividing the viruses into different subclasses and subtypes. Consequently, the epitopes which are of importance in this context are, in particular, not those which are also present in viruses of the HIV-1 and/or HIV-2 groups but rather those epitopes which occur only in the deposited virus according to the invention and in those variants which belong to the narrow group of the MVP-2901/94 virus. The morphological and immunological properties of the virus are also mirrored in the diagnostically relevant region of the coat protein.
The invention also embraces immunodeficiency viruses which exhibit an RNA sequence which possesses at least 75% homology, based on the entire genome, with the RNA of the deposited virus.
Preferred immunodeficiency viruses are those which exhibit an RNA sequence which possesses at least 85%, and particularly preferably at least 90%, homology, based on the entire genome, with the RNA of the deposited virus. Very particularly preferred immunodeficiency viruses are those which possess 92%, or even 95%, homology, based on the entire genome, with the RNA of the deposited virus.
The immunodeficiency viruses according to the invention exhibit an RNA sequence which is complementary to the DNA sequence in Table 1 and possesses at least 75% homology with this sequence in Table 1. In a preferred form, the immunodeficiency viruses according to the invention exhibit an RNA sequence which, is complementary to the DNA sequence in Table 1 and possesses at least 85% homology with the sequence in Table 1. In this context, the homologous moiety of the sequence is at least 50 nucleotides in length and, in a preferred embodiment, at least 100 nucleotides in length.
The immunodeficiency viruses according to the invention exhibit a sequence or a constituent sequence which is complementary to the sequence depicted in Table 1 or is homologous with this sequence, with the difference from the sequence given in Table 1, based on the diagnostically relevant region, being at most 20% at the nucleotide level and 25% at the protein level.
In a preferred embodiment, the difference from the sequence given in Table 1, based on the diagnostically relevant region, is at most 10% at the nucleotide level and 15% at the protein level.
The present invention also relates to a cDNA which is complementary to the RNA, or parts thereof, of the immunodeficiency virus MVP-2901/94, which is deposited at the European Collection of Animal Cell Cultures (ECACC) under No. V 95012601, or of a virus according to the invention.
In the preferred embodiment, this cDNA is in the form of recombinant DNA.
The invention also embraces antigens which are prepared using the cDNA according to the invention or the recombinant DNA, or using the amino acid structure which can be deduced from its cDNA. In this context, the antigen is a protein or peptide.
In a preferred embodiment, the antigens according to the invention exhibit an amino acid sequence which corresponds to the amino acid sequence depicted in Table 1 or to a constituent sequence thereof.
Preferably, the antigen exhibits a constituent sequence having at least 10 amino acids, particularly preferably having at least 20 amino acids, selected from the amino acid sequence in Table 1.
In a particularly preferred embodiment, the antigen according to the invention exhibits an amino acid sequence NQQLLNLWGCKGKLICYTSVKWN or a constituent sequence thereof having at least 10 consecutive amino acids.
The present invention also embraces antigens which are prepared from an immunodeficiency virus of this invention and are, for example, in the form of purified viral preparations. The antigen according to the invention is preferably prepared by recombinant means; however, it is also possible to prepare the antigen synthetically, for example by solid phase synthesis.
The invention also embraces test kits for detecting antibodies against viruses which cause immune deficiency, which contain at least one antigen according to the invention.
The test kits can be based on Western blots, ELISA tests or fluorescence antibody detection tests. Recently, it has emerged that those methods in which the viral nucleic acid, or a specific region thereof, is amplified are very sensitive and effective for diagnosing viruses, and in particular HIV viruses.
One of the known detection methods is the polymerase chain reaction (PCR). As an alternative to this, the competitive polymerase chain reaction can also be used for detecting HIV infections (for example AIDS (1993), 7, Suppl. 2; S 65-S 71).
Another detection method, which has recently gained in importance especially in relation to HIV diagnosis, is the NASBA (nucleic acid sequence-based amplification) method. This method is described, for example, in AIDS 1993, 7 (Suppl. 2): S 107-S 110. In this method, the single-stranded RNA, or else the double-stranded DNA, is amplified with T7 RNA polymerase and then detected.
A further method for detecting HIV viruses is that of detection by means of signal amplification using branched DNA. This is described, for example, in AIDS 1993, 7 (Suppl. 2): S 11-S 14. In this method, the viral nucleic acid is hybridized to probes which are bound to a solid phase. Furthermore, a detection molecule (branched DNA structures) is hybridized to the probe and then detected enzymically.
A feature shared in common by the above methods is that defined nucleic acid regions, which are specific for the virus to be detected, are employed in the detection methods. In the case of these detection methods, defined, short nucleic acid fragments, which are, in particular DNA fragments, are selected and employed in the detection methods.
The present invention also relates, therefore, to those nucleic acid fragments which exhibit a sequence which corresponds to a nucleic acid according to the invention or is complementary to this nucleic acid. These nucleic acid fragments, which can, for example, be primers, have, as a rule, a length of at least 15, preferably at least 25, and particularly preferably at least 35, nucleotides. These nucleic acid fragments may be used, in accordance with the invention, in methods for detecting HIV viruses.
The immunodeficiency viruses according to the invention, the cDNA according to the invention and the antigens may be used for detecting retroviruses which cause immune deficiency.
The antigens according to the invention, in particular, may be used for preparing vaccines.
The invention also relates to ribonucleic acid which encodes a virus according to the invention.
Within the scope of the present invention, a part of the coat protein was sequenced which is of particular relevance for diagnosis. This part is an envelope region which encompasses the area of the so-called V3 loop; the region which was sequenced within the scope of the present invention extends into the so-called gp 41 region.
Within the scope of the present invention, a part of the coat protein was first sequenced and it was established that this sequence exhibits only a relatively low degree of homology with the corresponding sequences of viruses of the HIV type. Comparison with HIV sequences, which was carried out using databases, indicated that the gp 41 region, in particular, was at most 79.1% homologous at the nucleotide level.
The sequence of the virus according to the invention differs from that of previously known viruses. The present invention relates, therefore, to those viruses, and corresponding DNA and amino acid sequences, which substantially correspond with the sequence of the virus according to the invention, with the degree of deviation being determined by the degree of homology. An homology of, for example, more than 85% denotes, therefore, that those sequences are encompassed in which at least 85 out of 100 nucleotides or amino acids are the same nucleotides or amino acids, while the remainder can be different. When homology is being established, the two sequences are aligned in such a way that the greatest possible number of nucleotides or amino acids which correspond to each other coincide with each other.
On the basis of the isolated, sequence, immunodominant epitopes (peptides) can be formulated and synthesized. Since the nucleic acid sequence of the virus is known, the person skilled in the art can deduce the amino acid sequence from this. A constituent region of the amino acid sequence is given in Table 1. The present invention also relates, therefore, to antigens, i.e. proteins, oligopeptides or polypeptides, which can be prepared using the information disclosed in Table 1. These antigens, proteins, polypeptides and oligopeptides exhibit amino acid sequences which are given in Table 1. The antigens or peptides can exhibit relatively short constituent sequences of an amino acid sequence which is reproduced in Table 1. This amino acid sequence is at least 10 amino acids, preferably at least 20, and particularly preferably at least 25, amino acids in length. In addition to using recombinant technology, these peptides can also be prepared by synthetic methods. A suitable route of preparation is solid phase synthesis of the Merrifield type. Further description of this technique, and of other methods which are known from the state of the art, can be found in the literature, for example M. Bodansky, et al., Peptide Synthesis, John Wiley and Sons, 2nd Edition 1976.
In the diagnostic tests, a serum sample from the person to be investigated is brought into contact with the protein chains of one or more proteins or glycoproteins (which can be expressed in eukaryotic cell lines), or parts thereof, which derive from MVP-2901/94. Test methods which are preferred include the immunofluoresence or immunoenzymic test methods (e.g. ELISA and immunoblot).
In the immunoenzymic tests (ELISA), antigen which derives from MVP-2901/94, or a variant thereof, can, for example, be bound to the walls of microtiter plates. The dose which is used in this context essentially depends on the test system and on the treatment of the microtiter plates. Serum, or serum dilutions, which derive from the person to be investigated are then added to the wells of the microtiter plates. After a defined incubation period, the plate is washed and specific immune complexes are detected with antibodies which bind specifically to human immunoglobulins and which have been linked beforehand to an enzyme, for example horseradish peroxidase, alkaline phosphatase, etc., or to an enzyme-labeled antigen. These enzymes can convert a colorless substrate into a highly colored product, and the presence of specific anti-HIV antibodies can then be determined from the intensity of the color. Another possible use for the virus according to the invention in test systems is its use in Western blots.
Even though it is proving extremely difficult to prepare vaccines against immunodeficiency diseases, this virus, or parts thereof, i.e. immunodominant epitopes and inducers of cellular immunity, or recombinantly prepared antigens, can, nevertheless, also be used to develop and prepare vaccines.